LED display device

• US 5,732,098 A
• Filed: 04/11/1996
• Issued: 03/24/1998
• Est. Priority Date: 04/14/1995
• Status: Expired due to Term

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Ishikawa, Masayuki, Nakamura, Takafumi, Saeki, Ryo, Iwamoto, Masanobu, Nisitani, Katsuhiko, Unno, Kazumi
• Primary Examiner(s): Lee, John D.
• Assistant Examiner(s): KIM, ELLEN E
• Application Number:
  US08/611,460
• Time in Patent Office: 712 Days
• Field of Search: 372/45, 372/46, 257/12, 257/15, 257/17, 257/183, 257/461, 257/94, 257/95, 257/97, 257/98
• US Class Current: 372/45.01
• CPC Class Codes: H01L 33/145 with a current-blocking structure
• CPC Class Codes: H01L 33/30 containing only elements of Group III and Group V of the Periodic Table

Abstract

A semiconductor light emitting device has a double heterostructure. The device is composed of an active layer and clad layers that sandwich the active layer. At least one of the clad layers has a multilayer structure having at least two element layers. The Al mole fraction of an element layer, which is proximal to the active layer, of the multilayer structure is smaller than that of the other element layer thereof distal from the active layer. This arrangement improves the crystal quality of an interface between the active layer and the clad layer of multilayer structure and effectively confines carriers in the active layer.

Claims

1. A light emitting diode for emitting spontaneous radiation and having a double heterostructure, comprising:

a) an active layer for emitting the spontaneous radiation having a give wavelength;

b) a first clad layer of a first conductivity type formed on the active layer;

c) a first clad layer of a second conductivity type formed under the active layer;

d) a second clad layer of the first conductivity type formed on the first clad layer of the first conductivity type;

e) a reflection layer formed under the first clad layer of the second conductivity type for vertically reflecting the spontaneous radiation;

f) a current block layer formed on a part of the second clad layer;

g) a current diffusion layer formed on the current block layer and on an exposed surface of the second clad layer; and

h) an upper metal electrode locally formed above or on a part of the current diffusion layer so to define an optical aperture for emitting the spontaneous radiation upwardly,

the forbidden band gap of the first clad layer of the first conductivity type being smaller than that of the second clad layer of the first conductivity type.

2. A diode of claim 1, wherein the active layer, the first and second clad layers of the first conductivity type, and the first clad layer of the second conductivity type are each made of compound semiconductor containing Al, the Al mole fraction of the active layer is smaller than that of the first clad layers of the first and second conductivity types, and the Al mole fraction of the second clad layer of the first conductivity type is larger than that of the first clad layer of the first conductivity type.

3. A diode of claim 2, wherein the Al mole fraction "x" of the active layer may take "0."

4. A diode of claim 2, wherein the Al mole fraction z of the second clad layer of the first conductivity type may take "1."

5. A diode of claim 1, wherein the second clad layer of the first conductivity type is made of n-type In₀.5 Al₀.5 P, the first clad layer of the first conductivity type is made of n-type In₀.5 (Ga₀.3 Al₀.7)₀.5 P, and the first clad layer of the second conductivity type is made of p-type In₀.5 (Ga₀.3 Al₀.7)₀.5 P.

6. A diode of claim 1, wherein the second clad layer of the first conductivity type is made of n-type. Al₀.2 Ga₀.8 N, the first clad layer of the first conductivity type is made of n-type Al₀.05 Ga₀.95 N, and the first clad layer of the second conductivity type is made of p-type Al₀.2 Ga₀.8 N.

7. A diode of claim 1, further comprising a second clad layer of the second conductivity type interposed between the first clad layer of the second conductivity type and the reflection layer, the forbidden band gap of the first clad layer of the second conductivity type being smaller than that of the second clad layer of the second conductivity type.

8. A diode of claim 7, wherein the first and second clad layers of the second conductivity type are each made of compound semiconductor containing Al, the Al mole fraction of the active layer being smaller than that of the first clad layer of the second conductivity type, the Al mole fraction of the second clad layer of the second conductivity type being larger than that of the first clad layer of the second conductivity type.

9. A diode of claim 8, wherein the Al mole fraction "x" of the active layer and the Al mole fraction "y" of the first clad layers of the first and second conductivity types are as follows:

space="preserve" listing-type="equation">x+0.1≦

y≦

x+0.5

and the thickness of each of the first .clad layers of the first and second conductivity types is in the range of 0.05 to 0.1 μ

m.

10. A diode of claim 8, wherein the Al mole fraction "z" of the second clad layer of the second conductivity type may take "1."

11. A diode of claim 7, wherein the total thickness of the first and second clad layers of the first conductivity type is 0.5 to 1.0 μ

m, and the total thickness of the first and second clad layers of the second conductivity type is 0.5 to 1.0 μ

m.

12. A diode of claim 7, wherein the first and second clad layers of the first conductivity type are made of p-type In₀.5 (Ga₀.3 Al₀.7)₀.5 P and p-type In₀.5 Al₀.5 P, respectively, and the first and second clad layers of the second conductivity type are made of n-type In₀.5 (Ga₀.3 Al₀.7)₀.5 P and n-type In₀.5 Al₀.5 P, respectively.

13. A diode of claim 7, wherein the first and second clad layers of the first conductivity type are made of p-type Al₀.05 Ga₀.95 N and p-type Al₀.2 Ga₀.8 N, respectively, and the first and second clad layers of the second conductivity type are made of n-type Al₀.05 Ga₀.95 N and n-type Al₀.2 Ga₀.8 N, respectively.

14. A diode of claim 7, wherein the first clad layer of the second conductivity type has one of monolayer and multilayer structures.

15. A diode of claim 7, wherein the Al mole fraction of the first clad layer of the second conductivity type gradually increases in proportion to the distance from the active layer.

16. A LED display device of claim 7, wherein a plurality of the light emitting diodes are arranged in an X-Y matrix to form a LED dot matrix circuit having data and scan lines.

17. A device of claim 16, wherein the light emitting diodes are connected to the intersections of the data and scan lines, respectively.

18. A device of claim 17 comprising a red LED dot matrix circuit having the light emitting diode emitting red light and a green LED dot matrix circuit having the light emitting diode emitting green light.

19. A diode of claim 1, wherein the first clad layer of the first conductivity type has one of monolayer and multilayer structures.

20. A diode of claim 1, wherein the Al mole fraction of the first clad layer of the first conductivity type gradually increases in proportion to the distance from the active layer.

21. A LED display device of claim 1, wherein a plurality of the light emitting diodes are arranged in an X-Y matrix to form a LED dot matrix circuit having data and scan lines.

22. A device of claim 21, wherein the light emitting diodes are connected to the intersections of the data and scan lines, respectively.

23. A device of claim 22 comprising a red LED dot matrix circuit having the light emitting diode emitting red light and a green LED dot matrix circuit having the light emitting diode emitting green light.

24. A device of claim 23 comprising a red LED dot matrix circuit having the light emitting diode emitting red light and a green LED dot matrix circuit having the light emitting diode emitting green light.

25. A diode of claim 1, wherein said upper metal electrode is locally formed above or on a central portion of said current diffusion layer.

26. A diode of claim 1, further comprising a contact layer interposed between said upper metal electrode and said current diffusion layer.

27. A light emitting diode for emitting spontaneous radiation and having a double heterostructure, comprising:

a) an active layer for emitting the spontaneous radiation having a given wavelength;

b) a first clad layer of a first conductivity type formed on the active layer;

c) a first clad layer of a second conductivity type formed under the active layer;

d) a second clad layer of the second conductivity type formed under the first clad layer of the second conductivity type;

e) a reflection layer formed under the second clad layer for vertically reflecting the spontaneous radiation;

f) a current block layer formed above or on the first clad layer of the first conductivity type;

g) a current diffusion layer formed on the current block layer and above or on the first clad layer of the first conductivity type; and

h) an upper metal electrode locally formed above or on a part of the current diffusion layer so to define an optical aperture for emitting the spontaneous radiation upwardly,

the forbidden band gap of the first clad layer of the second conductivity type being smaller than that of the second clad layer of the second conductivity type.

28. A diode of claim 27, wherein the active layer, the first clad layer of the first conductivity type, and the first and second clad layers of the second conductivity type are each made of compound semiconductor containing Al, the Al mole fraction of the active layer is smaller than that of the first clad layer of the second conductivity type, and the Al mole fraction of the second clad layer of the second conductivity type is larger than that of the first clad layer of the second conductivity type.

29. A diode of claim 27, wherein the second clad layer of the second conductivity type is made of n-type In₀.5 Al₀.5 P, the first clad layer of the second conductivity type is made of n-type In₀.5 (Ga₀.3 Al₀.7)₀.5 P, and the first clad layer of the first conductivity type is made of p-type In₀.5 Al₀.5 P.

30. A diode of claim 27, wherein the second clad layer of the second conductivity type is made of n-type Al₀.2 Ga₀.8 N, the first clad layer of the second conductivity type is made of n-type Al₀.05 Ga₀.95 N, and the first clad layer of the first conductivity type is made of p-type Al₀.2 Ga₀.8 N.

31. A diode of claim 27, wherein the Al mole fraction of the first clad layer of the second conductivity type gradually increases in proportion to the distance from the active layer.

32. A LED display device of claim 27, wherein a plurality of the light emitting diodes are arranged in an X-Y matrix to form a LED dot matrix circuit having data and scan lines.

33. A device of claim 32, wherein the light emitting diodes are connected to the intersections of the data and scan lines, respectively.

34. A device of claim 33 comprising a red LED dot matrix circuit having the light emitting diode emitting red light and a green. LED dot matrix circuit having the light emitting diode emitting green light.

35. A diode of claim 27, wherein said upper metal electrode is locally formed above or on a central portion of said current diffusion layer.

36. A diode of claim 27, further comprising a contact layer interposed between said upper metal electrode and said current diffusion layer.

37. A light emitting diode for emitting spontaneous radiation and having a double heterostructure, comprising:

a) an active layer for emitting the spontaneous radiation having a predetermined wavelength;

b) a clad layer of a first conductivity type formed on the active layer;

c) a clad layer of a second conductivity type formed under the active layer;

d) a reflection layer formed under the clad layer of the second conductivity type for vertically reflecting the spontaneous radiation;

e) a current block layer formed above or on the clad layer of the first conductivity type;

f) a current diffusion layer formed on the current block layer and above or on the clad layer of the first conductivity type; and

g) an upper metal electrode locally formed above or on a part of the current diffusion layer so to define an optical aperture for emitting the spontaneous radiation upwardly,

the Al mole fraction of the active layer side of at least one of the clad layers being smaller than that of the other side, which is distal from the active layer, of the same clad layer.

38. A diode of claim 37, wherein the Al mole fraction of at least one of the clad layers gradually increases in proportion to the distance from the active layer.

39. A LED display device of claim 37, wherein a plurality of the light emitting diodes are arranged in an X-Y matrix to form a LED dot matrix circuit having data and scan lines.

40. A device of claim 39, wherein the light emitting diodes are connected to the intersections of the data and scan lines, respectively.

41. A device of claim 40 comprising a red LED dot matrix circuit having the light emitting diode emitting red light and a green LED dot matrix circuit having the light emitting diode emitting green light.

42. A diode of claim 37, wherein said upper metal electrode is locally formed above or on a central portion of said current diffusion layer.

43. A diode of claim 37, further comprising a contact layer interposed between said upper metal electrode and said current diffusion layer.